Zanzibar City

Zanzibar City, Tanzania

Zanzibar City, a low lying city off the coast of Tanzania enjoys a historic heritage and functions as a hub of business and administration for the Zanzibar isles. However, as a highly dense city, with unplanned communities, and poor infrastructure, it is faced with a cyclic problem of urban flooding. Urban flooding has multiplier effect on people’s health, economic wellbeing and social interactions. Urban infrastructure is severely damaged by these floods, and households in the vulnerable zones are subjected to harsh disturbance during rains; including, but not limited to the destruction of property and population displacement. Habitual flooding is also correlated with cholera outbreaks in the fringes of the city.

In 2016, at the request of Zanzibar Commission for Lands (COLA), World Bank launched the Zanzibar Mapping Initiative (ZMI). The goal of ZMI was to update Zanzibar's existing aerial imagery with a newly acquired set at a spatial resolution of 7 cm per pixel, using only drones piloted by local teams. The imagery will be accessible to the OpenData community on a Geonode platform providing visualization and integration via online mapping services but also data access through download.
The Zanzibar Urban Planning Department, the Zanzibar Commission for Disasters as well as Municipal councils are engaging in sustainable planning in an attempt to reduce the impacts related to these recurring floods. The key project objective of Open Cities Zanzibar is to contribute to the development of Zanzibar’s resilience to urban flooding through the creation of ready to use, accessible spatial data; which will aid the planning process and subsequent interventions.

Mapping Progress to Date

This section provides an overview of mapping activities in the selected city geographic extent. The Before/After widget below allows comparing current density and distribution of map features with snapshots from previous years. The time chart of OSM editing activity over time offers insights on how many features have been contributed to the map over a specified period.

Data Quality

While OSM coverage keeps increasing, it's important to also understand quality of the data created. The tools available in this section allow for comparing OSM data with other "reference" datasets. These could be, for example, official datasets from government agencies showing distribution of features with those available OSM. The "Gap Detection" widget provides a visual representation of potential gaps in data, by comparing the latest OSM buildings with built-up areas automatically detected from satellite imagery.

OSM Community Dynamics

Understanding mapping progress and data quality also requires looking at the local OSM community and how mappers have contributed over time. Embedded widgets in this sections allow e.g. exploring the list of top mappers who contributed to features within the city extent, with links to their OSM user profile page. A time chart of number of user contributions over pre-defined time periods (daily, weekly, monthly), also provides a picture of how consistent the mapping activity in the area is.